April 15th, 2014
The journal of chemical education can be a fertile source of ideas for undergraduate student experiments. Take this procedure for asymmetric epoxidation of an alkene.[1] When I first spotted it, I thought not only would it be interesting to do in the lab, but could be extended by incorporating some modern computational aspects as well.
Read the rest of this entry »
References
- A. Burke, P. Dillon, K. Martin, and T.W. Hanks, "Catalytic Asymmetric Epoxidation Using a Fructose-Derived Catalyst", Journal of Chemical Education, vol. 77, pp. 271, 2000. https://doi.org/10.1021/ed077p271
Tags: chemical education, energy, free energy, Shi Fructose
Posted in Interesting chemistry, reaction mechanism | 2 Comments »
April 13th, 2014
Around 100 tons of the potent antimalarial artemisinin is produced annually; a remarkable quantity given its very unusual and fragile looking molecular structure (below). When I looked at this, I was immediately struck by a thought: surely this is a classic molecule for analyzing stereoelectronic effects (anomeric and gauche). Here this aspect is explored.
Read the rest of this entry »
Tags: C7 Lp, Cambridge, stereo-electronics
Posted in crystal_structure_mining, Interesting chemistry | No Comments »
April 10th, 2014
Science is rarely about a totally new observation or rationalisation, it is much more about making connections between known facts, and perhaps using these connections to extrapolate to new areas (building on the shoulders of giants, etc). So here I chart one example of such connectivity over a period of six years.
Read the rest of this entry »
Tags: ACS, electronics, higher energy, Steve Bachrach
Posted in Hypervalency, Interesting chemistry | No Comments »
April 6th, 2014
In the previous post, I showed how modelling of unbranched alkenes depended on dispersion forces. When these are included, a bent (single-hairpin) form of C58H118 becomes lower in free energy than the fully extended linear form. Here I try to optimise these dispersion forces by adding further folds to see what happens.
Read the rest of this entry »
Tags: energy, energy penalty, energy stabilisation, free energy, lowest-energy folding
Posted in General | No Comments »
March 29th, 2014
By about C17H36, the geometry of “cold-isolated” unbranched saturated alkenes is supposed not to contain any fully anti-periplanar conformations. [1] Indeed, a (co-crystal) of C16H34 shows it to have two-gauche bends.[2]. Surprisingly, the longest linear alkane I was able to find a crystal structure for, C28H58 appears to be fully extended[3],[4] (an early report of a low quality structure for C36H74[5] also appears to show it as linear).‡ Here I explore how standard DFT theories cope with these structures.
Read the rest of this entry »
References
- N.O.B. Lüttschwager, T.N. Wassermann, R.A. Mata, and M.A. Suhm, "The Last Globally Stable Extended Alkane", Angewandte Chemie International Edition, vol. 52, pp. 463-466, 2012. https://doi.org/10.1002/anie.201202894
- N. Cocherel, C. Poriel, J. Rault‐Berthelot, F. Barrière, N. Audebrand, A. Slawin, and L. Vignau, "New 3π‐2Spiro Ladder‐Type Phenylene Materials: Synthesis, Physicochemical Properties and Applications in OLEDs", Chemistry – A European Journal, vol. 14, pp. 11328-11342, 2008. https://doi.org/10.1002/chem.200801428
- S.C. Nyburg, and A.R. Gerson, "Crystallography of the even <i>n</i>-alkanes: structure of C<sub>20</sub>H<sub>42</sub>", Acta Crystallographica Section B Structural Science, vol. 48, pp. 103-106, 1992. https://doi.org/10.1107/s0108768191011059
- R. Boistelle, B. Simon, and G. Pèpe, "Polytypic structures of n-C28H58 (octacosane) and n-C36H74 (hexatriacontane)", Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, vol. 32, pp. 1240-1243, 1976. https://doi.org/10.1107/s0567740876005025
- H.M.M. Shearer, and V. Vand, "The crystal structure of the monoclinic form of n-hexatriacontant", Acta Crystallographica, vol. 9, pp. 379-384, 1956. https://doi.org/10.1107/s0365110x5600111x
Tags: dispersion, energy, relative energy, relative free energy
Posted in General | No Comments »
March 18th, 2014
OK, you have to be British to understand the pun in the title, a famous comedy skit about four candles. Back to science, and my mention of some crystal data now having a DOI in the previous post. I thought it might be fun to replicate the contents of one of my ACS slides here.
Read the rest of this entry »
Tags: ACS, DOI, Google, Handle, JSON, LOCATT
Posted in Chemical IT | 5 Comments »
March 12th, 2014
My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalyst-free bromination of benzene to give bromobenzene and HBr.
Read the rest of this entry »
Tags: activation energy, animation, aromatic, Boris Galabov, co-author, electrophilic, lowest energy solution, o/p director of aromatic electrophilic substitution, Paul Schleyer, pence, substitution
Posted in Interesting chemistry, reaction mechanism | 8 Comments »
March 8th, 2014
The diazo-coupling reaction dates back to the 1850s (and a close association with Imperial College via the first professor of chemistry there, August von Hofmann) and its mechanism was much studied in the heyday of physical organic chemistry.[1] Nick Greeves, purveyor of the excellent ChemTube3D site, contacted me about the transition state (I have commented previously on this aspect of aromatic electrophilic substitution). ChemTube3D recruits undergraduates to add new entries; Blue Jenkins is one such adding a section on dyes.
Read the rest of this entry »
References
- S.B. Hanna, C. Jermini, H. Loewenschuss, and H. Zollinger, "Indices of transition state symmetry in proton-transfer reactions. Kinetic isotope effects and Bronested's .beta. in base-catalyzed diazo-coupling reactions", Journal of the American Chemical Society, vol. 96, pp. 7222-7228, 1974. https://doi.org/10.1021/ja00830a009
Tags: covalent systems, first professor, free energy, Imperial College, lowest energy pose, Nick Greeves, professor of chemistry
Posted in reaction mechanism | 2 Comments »